Abstract

In order to study the influence of the charge of the counterion on promoting the extraction of either cobalt(II)-tris-thiocyanate species with one negative charge or double charged cobalt(II)-tetra-thiocyanate species, partition equilibria bave been studied at 25°C between an aqueous phase at a 3M ionic strength and dichloromethane in the presence of a divalent cation, , and as a function of the concentraction of thiocyanate and of a polyether (dicycloexyl-18-crown6) suitabie to be coordinated by barium. Being either thiocyanate or polyether absent, no appreciable extraction of both barium and cobalt has been observed into dichloromethane. When both are present, they mutually influence the barium and cobalt extraction, as the cationic 1: 1 barium-polyether and anionic 1: 4 cobalt-thiocyanate species, which are double-charged and give rise to an ion pair. The partition constant have been determined and the extraction mecanism has been discussed.